A period of sleep includes one or more cycles of different sleep stages that enable a person to recover mentally and physically. For example, rapid eye movement (REM) sleep is associated with strengthening memories, boosting mood, and consolidating information learned during the day. Non-rapid eye movement (NREM) sleep is associated with muscle and tissue recovery, stimulation of physical growth and development, and strengthening of the immune system. By tracking a person's total period of sleep and the corresponding progression through the stages of sleep, a sleep tracking system is able to determine if the person is getting an optimal amount of sleep for mental and/or physical recovery as well as diagnose sleep disorders.
Polysomnography (PSG) is a comprehensive recording of biophysiological changes that occur during sleep. For example, PSG may monitor activity of the brain, eye(s), muscle(s), and heart of a person during sleep. As a result, PSG is able to determine which portions of the person's sleep period are spent in the various stages of sleep. While often considered the “gold standard” of sleep monitoring, PSG may include monitoring a person in a laboratory setting. Such a setting is often expensive and may induce anxiety or otherwise discourage normal sleep period/cycles. Additionally, PSG includes attaching up to 22 electrodes to a person undergoing the sleep monitoring. Given the expensive and invasive nature of PSG, it is not ideal for persons seeking to track sleep on a regular basis in order to optimize sleep and the corresponding physical and mental recovery.